Vaccine effectiveness against Covid begins to wane from 10 weeks after the second dose, public health experts have said, as Government scientists warned that a return to office working could lead to a “rapid increase” in hospital cases.
A paper from Public Health England (PHE), sent to the Scientific Advisory Group for Emergencies (Sage) on Thursday, shows that the Pfizer and AstraZeneca vaccines begin to wane in effectiveness against symptomatic Covid from around 10 weeks after the second dose.
By around the 20-week mark, AstraZeneca is just over 50% effective while Pfizer is just over 70%.
However, the jabs are believed to still offer very good protection against hospital admission, in particular with the Pfizer vaccine, with effectiveness of around 95% beyond 20 weeks after vaccination.
With the AstraZeneca vaccine, there appears to be some waning to just under 80% effectiveness against hospital admission from more than 20 weeks.
The PHE document said the vaccines also appear to offer a high degree of protection against death.
It concluded: “Overall, the results indicate that there is waning of vaccine effectiveness against symptomatic disease with both the Pfizer and AstraZeneca vaccines from approximately 10 weeks after the second dose.
“This is most evident in older adults.
“There is some indication of waning against hospitalisation from 15 weeks after the second dose, in particular among recipients of the AstraZeneca vaccine, though this waning appears to be predominantly in clinical risk groups.”
It comes as a consensus statement from the Scientific Pandemic Influenza Group on Modelling operational sub-group (SPI-M-O), released on Tuesday but dated September 8, said there is still “the potential for another large wave of hospitalisations” as the pandemic continues.
“While the relationship between cases and hospitalisations has changed due to vaccination, increasing cases remain the earliest warning sign that hospital admissions are likely to rise,” it said.
SPI-M-O said the early use of measures to control spread, which could include continued homeworking, cut the need for tougher measures later on.
It added: “There is a clear consensus that continued high levels of homeworking has played a very important role in preventing sustained epidemic growth in recent months.
“It is highly likely that a significant decrease in homeworking in the next few months would result in a rapid increase in hospital admissions.
“As well as encouraging homeworking, more light-touch measures could include clear messaging that recommends people act cautiously, more widespread testing, a return to requiring all contacts of cases to isolate, and more mask-wearing.”
The document also suggested that a peak of infections may occur in October to December instead of August to October.
But it added: “The large-scale outbreaks that were considered feasible after taking Step 4 (of the road map) have not been seen and the population has not reduced their cautious behaviours as dramatically as was considered possible.
“Given the large number of infections that have occurred in recent months and the additional vaccine doses delivered, it is unlikely that the highest levels seen in Step 4 road map scenarios from July will be reached without waning immunity or a novel variant emerging.”
A separate document relating to a Sage meeting from September 9 said the epidemic is “entering a period of uncertainty”.
It added: “Key uncertainties include the potential impact of any waning of immunity and any significant changes in contact patterns associated with increased attendance at workplaces and reopening of education settings.
“It will take several weeks to be able to understand the full impact of any such changes.”
Sage stressed that “early, ‘low-cost’ interventions may reduce need for more disruptive measures” and avoid an “unacceptable” level of hospital admissions.
The group added: “Late action is likely to require harder measures.”
Sir Patrick Vallance echoed the concerns at a Downing Street press briefing on Tuesday, but said vaccines are still holding up “very well” against hospital admissions and death.
He said falling levels of immunity are most evident in those who are most vulnerable to Covid-19.
The chief scientific adviser said: “The waning of immunity is clear. It’s greater for infection than it is for the waning against hospitalisations and deaths, so they’re holding up very well.
“This is some waning. And that waning is most evident in the people who are most at risk.”
He was also confident booster shots would tackle the problem of declining resistance to Covid-19.
Sir Patrick said a round of third jabs for the vulnerable was expected to have a “very big knock-on effect for protection in terms of infection, hospitalisations and deaths”.
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