Herd Immunity
NIH Experts: The Concept of Classical Herd Immunity May Not Apply to COVID-19
"Dr. Fauci and his colleagues write that achieving classical herd immunity against SARS-CoV-2 is unlikely, due to a combination of factors that include features of the virus as well as current societal dynamics. These include the virus’ ability to continually mutate to new variants; asymptomatic virus transmission, which complicates public health control strategies; the inability of prior infection or vaccination to provide durable protection against reinfection; suboptimal vaccination coverage; and adherence to non-pharmacologic interventions."
Where is herd immunity?
Cases in US are going down, seemingly from herd immunity, but not in UK, why? Moderna booster recommended by US FDA Independent Advisory Panel (who is on the panel?) approved for over 65, high risk of severe illness, and hazardous work. Half dose. Pfizer and Moderna are both for profit. Moderna shows reduced antibodies after 6 to 8 months. Antibodies not the whole story. Antibody levels not good indicator of immunity levels. Also consider memory cells, memory t cells, killer cells, helper cells, memory B cells are more important in longevity of immune response. Immunity is a spectrum of responses. Specific response in NK cells as well. People from original trial had more breakthrough infections in July and August. In UK 93.6% testing positive for antibodies, rates of infection mean that people getting sick had antibodies but still got sick anyway.
Population Immunity and Covid-19 Severity with Omicron Variant in South Africa
Natural Immunity to COVID 19
Most children now have natural immunity
Infection generates natural immunity
Covid-19: CDC confirms it keeps no records of cases with natural immunity re-infecting themselves or infecting others
Update: NATURAL IMMUNITY (COVID) lawsuits currently taking place across US…
This CDC graph shows it was wrong to fire people with Natural COVID immunity last year
Dr Campbell presents data from the CDC that shows almost no difference in outcomes for people who have recovered from COVID and not been vaccinated with those who have, in terms of likelihood of infections and hospitalizations (starts at 3:33).
Researchers at Mt Sinai School of Medicine have been creating a registry of people who have recovered from COVID 19 in order to learn more about the long-term effects of the virus, as well as to study how long natural immunity lasts. They looked at around 700 patients who were not vaccinated and found that a year past recovery 80% to 90% had titer levels high enough to be protective. The findings were presented here.
Vaccinating people who have had covid-19: why doesn’t natural immunity count in the US?
"Antonio Bertoletti, a professor of infectious disease at Duke-NUS
Medical School in Singapore, has conducted research that indicates T
cells may be more important than antibodies. Comparing the T cell
response in people with symptomatic versus asymptomatic covid-19,
Bertoletti’s team found them to be identical, suggesting that the
severity of infection does not predict strength of resulting immunity
and that people with asymptomatic infections “mount a highly functional
virus specific cellular immune response."
"Gandhi thinks logistics is only part of the story. “There’s a very clear message out there that ‘OK, well natural infection does cause immunity but it’s still better to get vaccinated,’ and that message is not based on data,” says Gandhi. “There’s something political going on around that.”
Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination — Kentucky, May–June 2021 (this study was published in the CDC journal MMWR)
This type of study, which is called a case control study, is prone to bias because researchers use past data, which allows them to "cherry pick" which variables and time frames support their hypothesis. That is exactly what happened in this study- the researchers chose the time interval between May 1st and June 30 which represents the time period of the lowest case rates in Kentucky at pretty much anytime in the pandemic, so the time period that is least likely to represent the overall general patterns in the data. The study also used a very small sample size of only 246 case-patients (patients in the study group, not the controls). In the discussion section of this paper the authors list 5 limitations that this study has. The most significant one being "this is a retrospective study design using data from a single state
during a 2-month period; therefore, these findings cannot be used to
infer causation.". The other limitations listed include lack of confirmation that the patients experienced reinfection rather than a prolonged infection or shedding, that not all vaccination records for KY residents are in the database used, vaccinated people may have been less likely to get tested, or there may be some other confounding factor that was not controlled for in this study including any differences between behavior of vaccinated or vaccinated people that could also be relevant.
Prevalence and Durability of SARS-CoV-2 Antibodies Among Unvaccinated US Adults by History of COVID-19
"Although evidence of natural immunity in unvaccinated healthy US adults
up to 20 months after confirmed COVID-19 infection is encouraging, it is
unclear how these antibody levels correlate with protection against
future SARS-CoV-2 infections, particularly with emerging variants. The
public health implications and long-term understanding of these findings
merit further consideration."
Study finds previous COVID-19 infection, but not vaccination, improves performance of antibodies and potentially provides longer-term protection
"The authors conclude: “While the number of antibodies decrease with time
in both COVID-19 recovered (but never vaccinated) patients and
vaccinated (but never infected) individuals, the quality of antibodies
increases following infection but not after vaccination. People with
obesity have a significantly higher and sustained antibody-induced
immune response following infection. These results provide specific
characteristics of the immune response that may explain the differential
protection against COVID-19 in previously infected compared with
only-vaccinated individuals.”
expert reaction to conference abstract looking at antibodies and performance of antibodies after COVID-19 infection versus after vaccination (discusses the above study)“But generally, natural infection generates a broader and longer-lasting
set of immune responses to all the viral antigens – so this is not
really surprising. After all, our immune systems have evolved over
several million years to deal with all types of pathogens – so I would
expect natural immunity to outperform any vaccine-induced immunity over
the longer term.”
Severity of SARS-CoV-2 Reinfections as Compared with Primary Infections
George Mason University grants vaccine exemption following prof's lawsuit
"In the statement, the professor said his lawsuit has
"increased public awareness that vaccinating the naturally immune is
medically unnecessary." "I speak for tens of millions of Americans in
the same circumstances I am in," he said, "and I call on leaders across
the country to develop humane and science-based approaches as opposed to
one-size-fits-all policies."
Occurrence and significance of Omicron BA.1 infection followed by BA.2 reinfection
"To investigate this, we selected a subset of samples from more than 1,8
million cases of infections in the period from November 22, 2021, until
February 11, 2022. Here, individuals with two positive samples, more
than 20 and less than 60 days apart, were selected. From a total of 187
reinfection cases, we identified 47 instances of BA.2 reinfections
shortly after a BA.1 infection, mostly in young unvaccinated individuals
with mild disease not resulting in hospitalization or death."
Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections
"No discernible differences in protection against symptomatic BA.1 and
BA.2 infection were seen with previous infection, vaccination, and
hybrid immunity."
Necessity of COVID-19 vaccination in previously infected individuals
"Individuals who have had SARS-CoV-2 infection are unlikely to benefit
from COVID-19 vaccination, and vaccines can be safely prioritized to
those who have not been infected before."
The people with hidden immunity against Covid-19
It
has been noticed that many people who have recovered from COVID do not
show antibodies to the virus, and that many of those who do have
antibodies that last nor more than 3 months. This implies that
long-term immunity to COVID may not be based on antibody titers but
other mechanisms may be necessary or significant.
"When researchers tested blood samples taken years before the
pandemic started, they found T cells which were specifically tailored to
detect proteins on the surface of Covid-19".
"T cells are a kind of immune cell, whose main purpose is to identify and
kill invading pathogens or infected cells. It does this using proteins
on its surface, which can bind to proteins on the surface of these
imposters. Each T cell is highly specific – there are trillions of possible versions
of these surface proteins, which can each recognize a different target.
Because T cells can hang around in the blood for years after an
infection, they also contribute to the immune system’s “long-term
memory” and allow it to mount a faster and more effective response when
it’s exposed to an old foe. "
Some people test negative to the antibodies but positive for t-cells
that recognize COVID virus. This could mean that there is twice as
much natural immunity to the virus than previously thought. About 40 to
60% of unexposed people have these t-cells. This is causing some
researchers to refocus their attention onto t-cell based immunity as a
more promising road to meaningful treatment. To understand the
importance of t-cells (also called t-lymphocytes) look at patients in
late-stage AIDS- the unusual cancers, the fevers, fatigue, weight-loss.
sores, etc. The Oxford vaccine induces both an antibody and a t-cell
response. However in severely affected patients many of these cells
seem to be disappearing out of the blood stream. It has been suggested
that the cells may be moving to affected parts of the body. However
there also appears to be a pattern of necrosis happening at areas such
as the spleen where many t-cells are found. Necrosis of the spleen is
generally a sign of t-cell disease, such as AIDS. If t-cells are being
destroyed this could explain why the elderly are so much more effected.
Longitudinal
observation and decline of neutralizing antibody responses in the three
months following SARS-CoV-2 infection in humans
"Antibody responses to SARS-CoV-2 can be detected in most infected
individuals 10–15 d after the onset of COVID-19 symptoms. However, due
to the recent emergence of SARS-CoV-2 in the human population, it is not
known how long antibody responses will be maintained or whether they
will provide protection from reinfection. Using sequential serum samples
collected up to 94 d post onset of symptoms (POS) from 65 individuals
with real-time quantitative PCR-confirmed SARS-CoV-2 infection, we show
seroconversion (immunoglobulin IgM, IgA, IgG) in >95% of cases and
neutralizing antibody responses when sampled beyond 8 d POS. We show
that the kinetics of the neutralizing antibody response is typical of an
acute viral infection, with declining neutralizing antibody titres
observed after an initial peak, and that the magnitude of this peak is
dependent on disease severity. Although some individuals with high peak
infective dose (ID50 > 10,000) maintained neutralizing antibody titres >1,000 at >60 d POS, some with lower peak ID50
had neutralizing antibody titres approaching baseline within the
follow-up period. A similar decline in neutralizing antibody titres was
observed in a cohort of 31 seropositive healthcare workers. The present
study has important implications when considering widespread serological
testing and antibody protection against reinfection with SARS-CoV-2,
and may suggest that vaccine boosters are required to provide
long-lasting protection."
Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications
"The variations of SARS-CoV-2 specific NAbs in recovered COVID-19
patients may raise the concern about the role of NAbs on disease
progression. The correlation of NAb titers with age, lymphocyte counts,
and blood CRP levels suggested that the interplay between virus and host
immune response in coronavirus infections should be further explored
for the development of effective vaccine against SARS-CoV-2 virus.
Furthermore, titration of NAb is helpful prior to the use of
convalescent plasma for prevention or treatment."
SARS-CoV-2 Antibody Response in Persons with Past Natural Infection
"The most remarkable finding of this study was the significantly lower
neutralizing antibody titer after administration of a second dose of
vaccine in previously uninfected patients than the titer after only a
single dose of vaccine in previously infected participants. It is
unclear how the neutralizing antibody titers influence the ability of
the host to transmit the virus. These findings provide evidence that
after the administration of a single dose of vaccine, the humoral
response against SARS-CoV-2 in persons with a history of SARS-CoV-2
infection is greater than the response in previously uninfected
participants who have received a second dose."
Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections
"SARS CoV 2 naive vaccinees had a 13.06-increased risk for breakthrough infection with the Delta variant compared to those previously infected, when the first event (infection or vaccination) occurred during January and February of 2021. The increased risk was significant (P<0.001) for symptomatic disease as well."
Commentary from Dr Mobeen: This basically means that people who had a previous infection with SARS CoV2 had about 13 times greater immunity to future COVID infections compared to people who had received the full course of Pfizer vaccines at around the same time. Reinfections would largely have been Delta variant so this difference is especially significant. Dr Mobeen also points out that the paper is not saying that vaccines made things worse or didn't help, they also offered protection greater than if the person had no immunity for any source, they were just 13 times less effective than natural immunity. He also points out that this doesn't mean that getting infected is better somehow- it's still a serious disease.
Protection against the Omicron Variant from Previous SARS-CoV-2 Infection
"Overall, in a national database study in Qatar, we found that the
effectiveness of previous infection in preventing reinfection with the
alpha, beta, and delta variants of SARS-CoV-2 was robust (at
approximately 90%), findings that confirmed earlier estimates.
Such protection against reinfection with the omicron variant was lower
(approximately 60%) but still considerable. In addition, the protection
of previous infection against hospitalization or death caused by
reinfection appeared to be robust, regardless of variant."
"Across studies, the total number of PCR-positive or antibody-positive participants at baseline was 615,777, and the maximum duration of follow-up was more than 10 months in three studies. Reinfection was an uncommon event (absolute rate 0%-1.1%), with no study reporting an increase in the risk of reinfection over time. Only one study estimated the population-level risk of reinfection based on whole genome sequencing in a subset of patients; the estimated risk was low (0.1% [95% CI: 0.08-0.11%]) with no evidence of waning immunity for up to 7 months following primary infection. These data suggest that naturally acquired SARS-CoV-2 immunity does not wane for at least 10 months post-infection. However, the applicability of these studies to new variants or to vaccine-induced immunity remains uncertain."
SARS-CoV-2
infection rates of antibody-positive compared with antibody-negative
health-care workers in England: a large, multicentre, prospective cohort
study (SIREN)
"A previous history of SARS-CoV-2 infection was associated with an 84%
lower risk of infection, with median protective effect observed 7 months
following primary infection. This time period is the minimum probable
effect because seroconversions were not included. This study shows that
previous infection with SARS-CoV-2 induces effective immunity to future
infections in most individuals."
Risk of Reinfection After Seroconversion to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): A Population-based Propensity-score Matched Cohort Study
"Seroconversion after SARS-CoV-2 infection confers protection against
reinfection lasting at least 8 months. These findings could help global
health authorities establishing priority for vaccine allocation."
Natural immunity against COVID-19 significantly reduces the risk of reinfection:
findings from a cohort of sero-survey participants
"Conflicting reports on the persistence of antibody levels in individuals recovered from COVID-19
infection, suggest that the immunity against COVID-19 may not be lasting for long. In India, by 30th
June, 2021, not less than 30 million people were infected with COVID-19 and 0.39 million people
were reported to have lost their life to the disease in India. I the current study we followed up with a
subsample of our previous sero-survey participants to assess whether natural immunity against
SARS-CoV-2 was associated with a reduced risk of re-infection. We conducted telephonic interview
of a total of 3038 participants, out of which 2238 participants responded and 5 participants were
found to be not alive, as conveyed by their close relatives. There was a non-response rate of 26.1%.
Out of the 2238 participants, 1170 were sero-positive and 1068 were sero-negative for antibody
against COVID-19. Our survey found that only 3 individuals in the sero-positive group got infected
with COVID-19 whereas 127 individuals reported contracting the infection the sero-negative group.
Interestingly, from the 127 sero-negative individuals who later contracted COVID-19 infection, 30
needed hospitalization, out of which 12 were on oxygen therapy, four in ICU and one was on
ventilator. At the other hand, from the 3 sero-positives re-infected with COVID-19, one had
hospitalization, but didnnot require oxygen support or critical care. These findings reinforce the
strong plausibility that development of antibody following natural infection not only protects against
re-infection by the virus to a great extent, but also safeguards against progression to severe COVID-
19 disease"
SARS-CoV-2 antibodies protect against reinfection for at least 6 months in a multicentre seroepidemiological workplace cohort
"Identifying the potential for SARS-CoV-2 reinfection is crucial for
understanding possible long-term epidemic dynamics. We analysed
longitudinal PCR and serological testing data from a prospective cohort
of 4,411 United States employees in 4 states between April 2020 and
February 2021. We conducted a multivariable logistic regression
investigating the association between baseline serological status and
subsequent PCR test result in order to calculate an odds ratio for
reinfection. We estimated an odds ratio for reinfection ranging from
0.14 (95% CI: 0.019 to 0.63) to 0.28 (95% CI: 0.05 to 1.1), implying
that the presence of SARS-CoV-2 antibodies at baseline is associated
with around 72% to 86% reduced odds of a subsequent PCR positive test
based on our point estimates. This suggests that primary infection with
SARS-CoV-2 provides protection against reinfection in the majority of
individuals, at least over a 6-month time period."
Assessment of SARS-CoV-2 Reinfection 1 Year After Primary Infection in a Population in Lombardy, Italy
"The baseline demographic characteristics are shown in the Table.
The median (interquartile range) age of the patients was 59 (40-78)
years, but positive cases were older and geographically distributed more
in the industrial area of Legnano."
