People infected with COVID-19 in the past are likely to be
protected against reinfection for several months, a Public Health
England (PHE) study
has found, although experts cautioned those with immunity may
still be able carry the virus in their nose and throat and
therefore have a risk of transmitting to others.
PHE has been regularly
testing tens of thousands of health care workers across the UK
since June for new COVID-19 infections as well as the presence of
antibodies, which suggest people have been infected before.
SIREN
study leaders are clear this first report provides no evidence
towards the antibody or other immune responses from COVID-19
vaccines, nor should any conclusions to be drawn on their
effectiveness. The SIREN
study will consider vaccine responses later this year.
PHE scientists working
on the study have concluded naturally acquired immunity as a
result of past infections provide 83% protection against
reinfection, compared to people who have not had the disease
before. This appears to last at least for 5 months from first
becoming sick.
While the SIREN
study will continue to assess whether protection may last for
longer, this means people who contracted the disease in the first
wave may now be vulnerable to catching it again.
Between 18 June and 24 November, scientists detected 44 potential
reinfections (2 ‘probable’ and 42 ‘possible’ reinfections) out of
6,614 participants who had tested positive for antibodies. This
represents an 83% rate of protection from reinfection.
PHE also warned that
although those with antibodies have some protection from becoming
ill with COVID-19 themselves, early evidence from the next stage
of the study suggests that some of these individuals carry high
levels of virus and could continue to transmit the virus to
others.
It is therefore crucial that everyone continues to follow the
rules and stays at home, even if they have previously had
COVID-19, to prevent spreading the virus to others. Remember to
wash hands regularly, wear face coverings and make space from
others to help reduce the likelihood of passing on the virus.
It is vital that, with cases at their highest level to date and
the R number above 1 across the country, people do everything
that they can to avoid the risk of transmitting the virus to
other people.
Professor Susan Hopkins, Senior Medical Advisor at Public Health
England and the SIREN
study lead said:
This study has given us the clearest picture to date of the
nature of antibody protection against COVID-19 but it is
critical people do not misunderstand these early findings.
We now know that most of those who have had the virus, and
developed antibodies, are protected from reinfection, but this
is not total and we do not yet know how long protection lasts.
Crucially, we believe people may still be able to pass the
virus on.
This means even if you believe you already had the disease and
are protected, you can be reassured it is highly unlikely you
will develop severe infections but there is still a risk that
you could acquire an infection and transmit to others. Now more
than ever it is vital we all stay at home to protect our health
service and save lives.
We are immensely grateful to our colleagues in the NHS for
giving up their time to volunteer, and whose continued
participation at a time of great stress is making this research
possible.
PHE’s SIREN
(SARS-CoV-2 Immunity and Reinfection EvaluatioN) study has
performed regular antibody and PCR testing on 20,787
healthcare workers, including frontline clinical staff and those
in non-clinical roles, from 102 NHS trusts since the study
commenced in June. 6,614 of these participants tested positive
for COVID-19 antibodies upon recruitment.
Of the 44 potential reinfections identified by the study, 2 were
designated ‘probable’ and 42 ‘possible’, based on the amount of
confirmatory evidence available. If all 44 cases were confirmed,
it would represent an 83% rate of protection from reinfection,
while if only the 2 ‘probable’ reinfections were confirmed, the
rate would be 99%. Further research is ongoing to clarify this
range.
The study found that antibody protection after infection lasts
for at least 5 months, on average, and scientists are currently
studying whether protection may last for longer. This means that
many people who contracted the disease in the first wave may now
be vulnerable to catching it again.
Both of the 2 ‘probable’ reinfections reported having experienced
COVID-19 symptoms during the first wave of the pandemic, but were
not tested at the time. Both patients reported that their
symptoms were less severe the second time. None of the 44
potential reinfection cases were PCR tested during the first
wave, but all tested positive for COVID-19 antibodies at the
point of recruitment to the study.
This analysis occurred prior to the widespread dissemination of
the new variant VOC202012/01, further work is underway in the
laboratory to understand whether and to what extent antibodies
also provide protection from this variant and future analysis
will assess the impact of VOC202012/01 on symptomatic and
asymptomatic infections in healthcare workers.
The study will continue to follow participants for 12 months to
explore how long any immunity may last, the effectiveness of
vaccines and to what extent people with immunity are able to
carry and transmit the virus.
