Tier 3 may not work and we may need Tier 4 before Christmas says SAGE

Level 1 measures alone are not enough to prevent the rapid growth of coronavirus, and a fourth level may be needed in areas where level 3 restrictions are not sufficient, government scientific advisers have warned.

Sage’s scientific advisory panel said the levels implemented across England before the second national lockdown had an impact on viral transmission, with higher levels having more effect.

However, documents released by Sage on Monday state that Tier 1 measures alone “are not enough to keep the epidemic from growing rapidly.”

In a meeting on November 12, the group concluded that some models suggested a modest (about 10%) reduction in the reproduction number – the R-value – when moving from Tier 1 to 2.

In some places, Tier 2 could be enough to reduce R below 1, but this has not yet been observed, and would be the case if R was only slightly above 1 before Tier 2 was implemented, the scientists said.

The paper added, “This suggests that Tier 2 is the minimum intervention needed to maintain some degree of control over the transmission, although this would not be the case everywhere and considerable uncertainty exists.

“In most cases moving from Tier 1 to Tier 2 would slow growth rather than reverse it.”

A separate statement from the Scientific Pandemic Influenza Group on Modeling, Operational sub-group (SPI-MO) on Nov. 11 suggested that a “Tier 4” may be required in areas where Tier 3 restrictions do not reduce numbers.

It read: “There is a lot of uncertainty about the effect of tiers, especially Tier 3.

“Testing and tracking, including mass testing, is most effective when prevalence is low.

“Even the most effective testing and tracking system will have little impact if the number of caseloads is high.

“As the impact of the levels will vary depending on the characteristics of different areas, a ‘Tier 4’ should be considered for those parts of the country where Tier 3 cannot mitigate the epidemic.

“This is especially important in the run-up to the winter festival period when thinking about relaxation of measures. It is crucial to keep or reduce the incidence between now and then. “

Sage argued that it is unclear whether a basic Tier 3 restriction alone at a regional or national level would be sufficient to reduce R to below 1.

The November 12 documents stated: “It is almost certain that the prevalence will remain high in some parts of the country at the end of the current national restrictions.

“When policymakers plan transitions from national measures to local approaches, or between levels in the future, both the prevalence and growth rate of new infections must be taken into account.”

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